                1. Field of the Invention        
The invention relates to a fixing system for printed circuit boards arranged one above the other in an electronics housing, especially for the automotive industry.
As a result of increasing demands imposed on the functionality of electronic control units in the field of engine management, devices are increasingly being designed with a number of printed circuit boards. In such cases conflicting requirements are increasingly arising as regards the mechanical design. On the one hand the electronics must be well cooled, meaning that only narrow and not very variable gaps are able to be considered for a thermal transition region. On the other the printed circuit boards should not be distorted mechanically in order to avoid reliability problems resulting from broken components or connections between components and printed circuit boards. The even spacings for a thermal transition region can be implemented by screwing the individual printed circuit boards onto the heat sink in a defined manner. However a relatively large amount of space on the printed circuit boards is used for the fixing elements. There are also technical layout restrictions to be considered because of the numerous large breakthroughs in the printed circuit boards. If the connecting elements are reduced there must be common fixings to the remaining two printed circuit boards. The result of this is that different gaps are produced by different tolerance chains and thus also a different thermal efficiency.
In this connection a system is known from DE 101 34 562 A1 for electrical contacting and mechanical fixing of printed circuit boards, which features at least one cutting element or insulation piercing connecting element for placement on the underside of a printed circuit board and a fixing element on the printed circuit board. In order to ensure a simple and fast assembly or disassembly, a support is fixed with regard to at least one conducting wire in such a manner that when mechanically fixing the printed circuit board to the support by means of the fixing element situated on the printed circuit board, the at least one conducting wire can be directly contacted essentially at the same time by means of the cutting element or insulation piercing connecting element on the underside of the printed circuit board.
The disadvantage of the prior art is that rigidly-mounted printed circuit boards will be deformed under the effect of heat, which can damage the electrical components on the circuit board or the electrical contacting. The non-stress-free support of the printed circuit boards when affected by heat also means that it is not possible to guarantee a thermally-optimized construction with defined thermal transition regions. Added to this is the fact that the mounting space on the circuit board is significantly restricted by the screw fixings.